Copyright Goodheart-Willcox Co., Inc. 96 Programmable Logic Controllers: Hardware and Programming 0000 0001 Pushbutton Switch (SW1) Limit switch (LS1) Motor Red_PLT O:0 I:0 I:0 I:0 O:0 2 1 0 0 1 End Goodheart-Willcox Publisher Figure 6-12. PLC ladder logic diagram for the relay logic diagram displayed in Figure 6-9. 6.3 Programming Ladder Logic Diagrams with Normally Open and Normally Closed Contacts Figure 6-13 displays a relay logic diagram in which an electric motor remains energized to operate in a continuous mode. When the motor is not energized, the green light is on. Pressing the start pushbutton turns the motor on. When the motor is energized, its associated normally open contact closes. Therefore, the motor runs until the stop pushbutton is closed. Also, when the motor is energized, its associated normally closed contact opens to turn off the green light. The modular Allen-Bradley SLC 5/03 PLC will be used to create the PLC ladder logic diagram for the relay logic diagram displayed in Figure 6-13. The software allows you to set up the I/O configuration. Figure 6-14 shows the selection of processor type 1747-L532 with a four slot chassis. Recall that slot zero is always reserved for the PLC processor. Slot one houses a 16-port 120 VAC input module. See Figure 6-15. Slot two houses a 16-port 120 VAC output module. See Figure 6-16. Goodheart-Willcox Publisher Figure 6-14. Select processor type 1747-L532 with four expansion slots. Stop Start M1 1, 2 M1 M1 L1 L2 G 1 2 Goodheart-Willcox Publisher Figure 6-13. Relay logic diagram.